The lilac is a deciduous, multi-stemmed shrub with an irregular, rounded outline. It is fast growing when young, but slows to about one foot a year with age. The stems are dark gray to gray-brown, and the wood is strong. The leaves are dark green to blue-green above and pale green below. In shades of lilac, light purple, or lavender, the clusters of four petal flowers bloom in April or May. They are extremely fragrant, While the lilac grows best in sunny sites, it will not tolerate hot, humid conditions. It prefers well drained, moist soil with a neutral or slightly alkaline pH. The soil can be supplemented with peat or leaf mold. Old flowers should be removed as soon as they fade.
The best time to prune lilacs is just flowering. It is preferable to prune the shrub to emphasize medium-aged wood, which will produce good blooms and still lend good size to the plant. To do this, remove one-third of the oldest stems at ground level every year. At the same time, any corrective pruning, such as removing conflicting branches or sucker growth can be done. Older lilacs that are a major landscape feature can be pruned as small multiple-branched trees, removing sucker growth and emphasizing a few large, old trunks. The shrub also can be trimmed into a single stemmed tree. Overgrown lilacs can be cut to within a few inches of the ground. Within 3-4 years, they will flower again, For a hedge, plant about 3-4 feet apart depending upon the mature height.